Ruled Out

The Sun

The facts: Since the 1970s, the sun has been cooling slightly. Over this same time period, the Earth has gotten warmer. Most of the warming has occurred in the lower atmosphere near the Earth's surface.

Could the sun be responsible for today's climate change?

No. If the sun were the cause of climate change, the Earth's temperature would be cooling, not warming! Also, if the sun were responsible for the increased warming, it would occur throughout the entire atmosphere.

So, the sun is NOT the cause of today's climate change.

The Earth's Orbit

The facts: The way the Earth tilts on its axis and the way it circles the sun can influence the amount of the sun's energy that reaches the planet. As a result, changes in the Earth's orbit can cause the climate to change, but these changes happen very slowly, over tens to hundreds of thousands of years.

Could the Earth's orbit be responsible for today's climate change?

No. Cycles in the Earth's orbit happen so slowly that they cannot account for the rapid warming we are seeing today. Also, the current position of the Earth's orbit should result in cooler temperatures, but instead, the opposite is happening—the average temperature of the Earth is getting warmer.

So, the Earth's orbit is NOT responsible for today's climate change.

Volcanoes

The facts: When volcanoes erupt, they add a small amount of greenhouse gases into the atmosphere. They also release dust, ash, and other particles called aerosols. Some volcanic explosions are so strong that they throw these aerosols high enough into the atmosphere that they block some sunlight from reaching the Earth.

Could volcanoes be responsible for today's climate change?

No. Although volcanoes do add some carbon dioxide (a greenhouse gas) into the atmosphere, people add about 100 times more! The amount of carbon dioxide that comes from volcanoes has not increased, and it's not enough to cause global warming. Actually, the main way volcanoes can change the Earth's climate is by causing a temporary cooling effect. After a very large eruption, particles from the eruption can stay in the atmosphere for as long as a few years, where they block sunlight and make the planet a little bit cooler. This has happened several times in the last 40 years—most recently in 1991 with the eruption of Mount Pinatubo in the Philippines.

So, volcanic eruptions are NOT responsible for today's climate change.